Soil Carbon Under Native and Exotic Trees on a Pastoral Dairy Farm in New Zealand
Year: 2026
Type: article
Abstract: Intensive dairying emits greenhouse gases and degrades waterways through nutrient runoff and leaching. Trees and shrubs on paddock margins may slow nutrient movement by raising infiltration and by immobilising nutrients in soil carbon. We measured soil carbon along transects running from pasture into three clusters on a pasture-based, intensively managed dairy farm near Lincoln, New Zealand: a mixed New Zealand native planting of nine species (Site MN), a hybrid willow, Salix matsudana × S. alba (Site W), and a planting of Kunzea robusta (kānuka) and Leptospermum scoparium (mānuka) (Site KM). Each planting type occurs at one site, so the study compared three case-study plantings, rather than native and exotic trees in general. Within these plantings, we tested four hypotheses: soil organic carbon (SOC) stock is higher under trees than under pasture (H1); particulate organic carbon (POC) concentration is higher under trees than under pasture (H2); SOC peaks at the dripline (H3); and SOC is higher under exotic trees than under New Zealand natives (H4). Carbon stocks over 0–0.3 m were significantly greater 12 m inside the mixed native planting, at 114 t C ha−1, than at the dripline and in the adjacent pasture, 95 t C ha−1, an increase of 20%. Stocks under willow and under kānuka/mānuka did not differ significantly from pasture. POC varied significantly with location under all three plantings at both 0–0.1 m and 0.1–0.3 m, and mean POC under the trees exceeded that under the adjacent pasture at every site and depth. In the 0–0.1 m layer POC averaged 0.22 to 0.35 g per 100 g of soil under the trees compared to 0.06 to 0.11 g per 100 g of soil under pasture. No planting had its highest carbon at the dripline, and the exotic willow had no more carbon than the natives, so H3 and H4 were not supported in these plantings. Tree clusters on paddock boundaries and marginal land add POC to agricultural landscapes at no cost to soil carbon. Future work should determine whether that carbon immobilises mobile nitrogen and phosphorus.
Source: Environments
Language: English
Subfield: Soil Science
Domain: Life Sciences
Open Access status: gold
Estimated APC paid: $2,172
OpenAlex ID: W7212289611